Wireless communication device that is capable of improving data transmission efficiency, associated network, and method

ABSTRACT

A wireless communication device includes a data transmission and reception section that wirelessly transmits a plurality of test packets; a signal sensing section that senses a power of a spatial radio wave signal on a frequency channel that is the same as the plurality of test packets and outputs sample data of the sensed spatial radio wave signal; a calculation processing section that converts the sample data into time series sample data; a collision detection section that calculates a packet collision rate based on the number of packet collisions and the number of the plurality of test packets if there is a packet collision due to interference of the plurality of test packets with another communication; and a control section that adjusts a parameter that the data transmission and reception section uses based on a calculation result of the collision detection section.

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2011-132314 filed on Jun. 14, 2011, thecontent of which is incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication device, anetwork, a wireless communication method, and a program that causes acomputer to execute the method.

2. Description of Related Art

In recent years, wireless LAN (Local Area Network) communication hasbecome common not only in companies' workplaces, but also in a varietyof fields including homes and outdoors. Because the use of wireless LANhas become widespread, there has been an increase in the traffic inavailable frequency resources, that are limited, thereby creatingserious concern about communication interference.

IEEE 802.11, which is one of the wireless LAN standards, uses an accesscontrol technique that is referred to as carrier sense multiple accesswith collision avoidance (CSMA/CA). This access control technique has afeature in which each wireless communication device starts communicationafter determining whether or not the neighboring wireless communicationdevices are generating radio waves.

In the foregoing access control technique, to avoid a communicationcollision, a wireless communication device of interest determineswhether or not a neighboring device (another wireless communicationdevice) is generating a radio wave. If the neighboring device isgenerating a radio wave, the device of interest waits for apredetermined time (back-off time) and then determines again whether ornot the neighboring device is generating a radio wave. If theneighboring device is not transmitting a radio wave, the device ofinterest transmits a radio wave after the elapse of a random time. Thewireless communication device of interest uses a carrier sense scheme soas to determine whether or not the neighboring device is generating aradio wave.

In the carrier sense scheme, the wireless communication device checksfor the use of a radio channel. If the device detects the preamble of asignal that complies with the IEEE 802.11 standard (synchronizationestablishment signal), since the device receives the signal, the radiochannel becomes busy. If the wireless communication device cannotreceive the preamble of the signal that complies with the IEEE 802.11standard and detects a power level that is greater than a predeterminedcarrier sense threshold, the wireless communication device determinesthat the radio channel is busy and waits to transmit a signal. Incontrast, if the wireless communication device detects a power levellower than the predetermined carrier sense threshold, the wirelesscommunication device determines that the radio channel is idle.

The foregoing access control technique has the following problem. In thefollowing description, a wireless communication device that complieswith IEEE 802.11 is referred to as “802.11 wireless device.”

The CSMA/CA scheme used to control transmission and reception for an802.11 wireless device has a problem in which, due to an externalinterference, a packet collision cannot be fully avoided. In addition,since a packet collision cannot be detected, if a communication failureoccurs due to a packet collision, the cause of the communication failurecannot be identified and thereby effective prevention measures cannot beimplemented. If a packet collision occurs due to external interference,since there are no means to quantitatively calculate the collision rate,it is difficult to accurately evaluate the collision rate.

A packet collision detection technique disclosed in JP 09-64884APublication (hereinafter referred to as Patent Literature 1)simultaneously transmits a signal and observes the signal over atransmission path, removes the transmission signal from the observedsignal, and determines whether or not a signal collision occurs over thetransmission path based on the energy amount of the signal from whichthe transmission signal was removed.

An alternative packet detection technique disclosed in JP 2010-23387APublication (hereinafter referred to as Patent Literature 2) calculatesdata collision likelihood based on the number of neighboring wirelessterminals, radio transmission rates, and so forth.

Although the technique disclosed in Patent Literature 1 can determinewhether or not there is an interference signal other than a transmissionsignal, it cannot determine whether or not the measured interferencesignal interferes with a signal received on the reception side. Inaddition, although a signal that the transmission side cannot measuremay interfere with a signal received on the reception side, thetechnique cannot detect the interference.

The technique disclosed in Patent Literature 2 calculates the datacollision likelihood based on the predicted wireless communicationstate. If the predicted wireless communication state largely differsfrom the real wireless communication state, the calculated collisionrate will not comply with the real wireless communication state. Thetechniques disclosed in Patent Literature 1 and Patent Literature 2 cannot detect packet collisions with sufficient accuracy. Thus,countermeasures to improve data transmission efficiencies cannot betaken.

In addition, the influence of external interference of wireless LANcommunication depends on the interference distance and the powerintensity of the interference wave. Thus, an 802.11 wireless devicecannot accurately identify such different interference states. As aresult, countermeasures to improve data transmission efficiencies cannotbe taken based on interference states.

SUMMARY

An object of the present invention is to provide a wirelesscommunication device, a network, and a wireless communication methodthat can suppress interference with another communication and that canallow data transmission efficiencies to improve, and also a program thatcan cause a computer to execute the method.

A wireless communication device according to the present inventionincludes a data transmission and reception section that wirelesslytransmits a plurality of test packets; a signal sensing section thatsenses a power of a spatial radio wave signal on a frequency channelthat is the same as the plurality of test packets and outputs sampledata of the sensed spatial radio wave signal; a calculation processingsection that converts the sample data that are output from the signalsensing section into time series sample data in which the sample dataare plotted in time series; a collision detection section thatdetermines whether or not there is a packet collision due tointerference of the plurality of test packets with another communicationbased on the time series sample data and calculates a packet collisionrate based on the number of packet collisions and the number of theplurality of test packets that have been transmitted if the packetcollision occurs; and a control section that adjusts a parameter thatthe data transmission and reception section uses to transmit data basedon a calculation result of the collision detection section.

The above and other objects, features and advantages of the presentinvention will become apparent from the following description withreference to the accompanying drawings which illustrate examples of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example of a structure of awireless communication device according to a first embodiment;

FIG. 2 is a schematic diagram showing an example of a communicationstate categorization algorithm executed by the wireless communicationdevice according to the first embodiment;

FIG. 3 is a schematic diagram showing the dependency of threshold B usedin the communication state categorization algorism shown in FIG. 2 onwireless transmission rates;

FIG. 4 is a schematic diagram specifically describing an operation of acommunication state categorization method performed by the wirelesscommunication device according to the first embodiment;

FIG. 5 is a schematic diagram showing an example of parameter be ofwireless device A shown in FIG. 4;

FIG. 6 is a schematic diagram showing an example of parameter dr ofwireless device A shown in FIG. 4;

FIG. 7 is a schematic diagram showing an example of a categorized resultof communication states of wireless device A shown in FIG. 4;

FIG. 8 is a schematic diagram showing an example of an interferencedetection algorithm executed by the wireless communication deviceaccording to the first embodiment;

FIG. 9A to FIG. 9D are schematic diagrams describing a method thatdetects a packet collision from time series sample data of powers;

FIG. 10A to FIG. 10D are schematic diagrams describing two types ofestimated packet collision patterns;

FIG. 11 is a schematic diagram showing a procedure of a communicationcontrol operation in which the wireless communication device accordingto the first embodiment identifies one communication state when acommunication state has been updated;

FIG. 12 is a schematic diagram showing a procedure of a communicationcontrol operation in which the wireless communication device accordingto the first embodiment identifies two communication states when acommunication state has been updated;

FIG. 13 is a block diagram showing an example of a structure of awireless communication device according to a second embodiment;

FIG. 14 is a block diagram showing an example of a structure of awireless communication device according to a third embodiment;

FIG. 15 is a schematic diagram showing an example of a mesh networkaccording to a fourth embodiment, the mesh network having the wirelesscommunication devices according to the first embodiment as basestations;

FIG. 16 is a schematic diagram describing an adjustment method forcarrier sending sensibilities of the base stations in the mesh networkaccording to the fourth embodiment;

FIG. 17 is a schematic diagram describing a communication qualitymeasurement method for communication paths in the mesh network accordingto the fourth embodiment; and

FIG. 18 is a sequence chart describing an operation method for the meshnetwork according to the fourth embodiment.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Next, a wireless communication device that complies with the 802.11wireless LAN standard as an embodiment of the present invention will bedescribed. In the following, a wireless communication device thatcomplies with IEEE 802.11 is referred to as “802.11 wireless device, “awireless transmission device that complies with IEEE 802.11 is referredto as “802.11 wireless transmission device,” and a wireless receptiondevice that complies with IEEE 802.11 is referred to as “802.11 wirelessreception device.”

First Embodiment

Next, a structure of the wireless communication device according to afirst embodiment will be described. FIG. 1 is a block diagram showing anexample of the structure of the wireless communication device accordingto this embodiment.

As shown in FIG. 1, the wireless communication device according to thisembodiment has communication section 1 that performs data communicationand signal sensing; calculation processing section 2 that performs aninitial process for a reception signal and calculates communicationevaluation parameters; storage section 3 that stores information;communication state categorization section 4 that categorizes thecommunication state of its own device that suffers from interferencewith another communication; collision detection section 5 that detects acommunication collision and evaluates it; and control section 6 thatadjusts communication performance of communication section 1.

Arithmetic control section 8 includes calculation processing section 2,communication state categorization section 4, collision detectionsection 5, and control section 6. Arithmetic control section 8 isprovided with a CPU (Central Processing Unit) (not shown) that executesa process according to a program; and memory (not shown) that stores theprogram. Calculation processing section 2, communication statecategorization section 4, collision detection section 5, and controlsection 6 are virtually configured by the CPU that executes the program.

Communication section 1 has signal sensing section 11 and datatransmission and reception section 12. Signal sensing section 11 isprovided with a reception antenna. Signal sensing section 11 senses thepower of a spatial radio wave signal in a frequency region that is thesame as the frequency channel that the wireless communication deviceaccording to this embodiment uses when it transmits a signal.

Data transmission and reception section 12 is provided with atransmission and reception antenna. Data transmission and receptionsection 12 transmits and receives data and test packets that thewireless communication device according to this embodiment processes andgather statistics of transmission and reception parameters with respectto packets that are transmitted and received. Transmission and receptionparameters are, for example, “a time that a transmission packetoccupies,” “a time after the first packet of a set of data istransmitted until the last packet is transmitted,” “the number oftransmission packets,” “the number of transmission success packets,” and“the number of transmission packets per unit time.”

Calculation processing section 2 converts power data of the spatialradio wave signal supplied form signal sensing section 11 into timeseries data and calculates communication evaluation parameters based onthe transmission and reception parameters supplied from datatransmission and reception section 12. The communication evaluationparameters are, for example, “Busy Count (bc),” “Delivery Ratio (dr),”“Standard Deviation of delivery ratios (Std(dr)).”

Parameter bc represents the ratio of a time for which it is determinedthat a channel of interest is likely to be used. Parameter bc isobtained by dividing a time for which the channel of interest is busy bythe measurement time. Parameter bc may be referred to as busy rate. Ifparameter bc cannot be continuously measured, it may be obtained bysampling the channel in the measurement time, counting the number ofsamples for which the channel is busy, and dividing the number ofsamples for which the channel is busy by the number of samples in themeasurement time. Parameter dr represents a transmission success rate.Parameter dr is given by formula (1) that follows.

$\begin{matrix}\left\lbrack {{Mathematical}\mspace{14mu} {Expression}\mspace{14mu} 1} \right\rbrack & \; \\{{dr} = \frac{TxFrame}{TxCount}} & {{Formula}\mspace{14mu} (1)}\end{matrix}$

where TxFrame is the number of transmission success packets in themeasurement time and TxCount is the number of transmission packets inthe measurement time.

Parameter Std(dr) represents the standard deviation of delivery ratios(dr) in a constant time.

Communication state categorization section 4 determines in which one ofthree states of its own device lies due to the influence of interferenceof its transmission with another communication. The three statescategorized by the communication evaluation parameters are “PerformanceAnomaly State (PA),” “Gray State (Gray),” and “Max Performance State(Good).”

State PA represents a communication state in which a high speedtransmission communication device and a low speed transmissioncommunication device can detect each other and the throughput of thehigh speed transmission communication device is lower than thethroughput of the low speed transmission communication device. In thiscontext, the throughput represents the effective transmission amount ofdata per unit time. State Gray represents a communication state in whicha transmission signal of an 802.11 wireless device X is not detected byanother 802.11 wireless device Y, the transmission signal of the 802.11wireless device X interferes with a transmission signal of the 802.11wireless device Y. In state Gray, the communication success rate becomeslower due to interference with another communication. State Goodrepresents a communication state in which a 802.11 wireless transmissiondevice uses a whole channel or another transmission device thattransmits a signal at the same rate as its own device uses the channel.

Collision detection section 5 has a means that calculates the number oftest packets that the wireless communication device according to thisembodiment transmits from the time series powers of the spatial radiowave signal that is output from calculation processing section 2; ameans that detects collisions of test packets transmitted by thewireless communication device according to this embodiment and datapackets transmitted by another wireless communication device; a meansthat calculates the number of collided data packets; and a means thatcalculates a collision rate of data packets based on the number ofcollided data packets and the number of test packets that the wirelesscommunication device according to this embodiment transmits.

Control section 6 adjusts the transmission parameters based on theresults that are output from communication state categorization section4 and collision detection section 5 so as to improve the transmissionefficiency of the wireless communication device according to thisembodiment. According to this embodiment, communication statecategorization section 4 and collision detection section 5 mayindependently or simultaneously operate so as to improve thetransmission efficiency.

Next, with reference to FIG. 1, the operation of the wirelesscommunication device according to this embodiment will be described indetail. First, the communication state categorization operation of thewireless communication device according to this embodiment will bedescribed in detail.

Data transmission and reception section 12 shown in FIG. 1 executes testtransmission for an 802.11 reception device at a constant transmissionrate. After data transmission and reception section 12 has executed testtransmission, it gathers statistics of the transmission and receptionparameters and outputs the statistical result of the transmission andreception parameters to calculation processing section 2.

Thereafter, calculation processing section 2 calculates communicationevaluation parameters bc, dr, and Std(dr) that serve to evaluate thetransmission result of the foregoing test transmission based on thestatistical results of the transmission and reception parameterssupplied from data transmission and reception section 12. Thereafter,calculation processing section 2 stores the calculated results of thecommunication evaluation parameters to storage section 3.

Thereafter, communication state categorization section 4 storescommunication evaluation parameters bc, dr, and Std(dr) that serve toevaluate test transmission to a buffer (not shown) provided incommunication state categorization section 4 so as to categorize thecommunication state of the wireless communication device according tothis embodiment. The communication state of the wireless communicationdevice according to this embodiment is categorized as one of threestates according to the communication state categorization algorithmshown in FIG. 2 due to the influence of the foregoing externalinterference. The three communication states are PA, Gray, and Good.

Next, with reference to FIG. 2, the communication state categorizationalgorithm will be described in detail. Communication statecategorization section 4 is virtually configured by the CPU (not shown)that is provided in arithmetic control section 8 and that executes aprogram containing the communication state categorization algorithmshown in FIG. 2. Thus, in the following, it is assumed that the subjectthat executes the communication state categorization algorithm shown inFIG. 2 is communication state categorization section 4.

Communication state categorization section 4 determines whether or notparameter dr is greater than threshold A (at step A1). If parameter dris greater than threshold A, communication state categorization section4 determines whether or not parameter bc is greater than threshold B (atstep A2). If parameter bc is greater than threshold B and parameter dris greater than threshold A, communication state categorization section4 detects that the communication state of the wireless communicationdevice according to this embodiment lies in state PA due to theinfluence of an external interference signal (at step A5). State PAcorresponds to a communication performance anomaly state in which,although the influence of interference with another communication is notlarge, a communication anomaly occurs.

In FIG. 2, if parameter dr is greater than threshold A at step A1 and ifparameter bc is equal to or smaller than threshold B at step A2,communication state categorization section 4 determines that thecommunication state of the wireless communication device according tothis embodiment lies in state Good in which the influence of theexternal interference signal is small (at step A4). State Goodcorresponds to a non-interference state in which the influence ofinterference with another communication hardly occurs.

If parameter dr is equal to or smaller than threshold A at step A1 shownin FIG. 2, communication state categorization section 4 determineswhether or not parameter Std(dr) is greater than threshold C (at stepA3). If parameter Std(dr) is greater than threshold C and parameter dris not greater than threshold A, communication state categorizationsection 4 detects that the communication state of the wirelesscommunication device according to this embodiment lies in state Gray dueto the influence of an external interference signal (at step A6). Thezone of state Gray is denoted by GZ. State Gray corresponds to acommunication interference state in which interference with anothercommunication occurs.

In FIG. 2, if parameter dr is equal to or smaller than threshold A andparameter Std(dr) is equal to or smaller than threshold C at step A1shown in FIG. 2 (at step A3), communication state categorization section4 determines that the test transmission signal of the wirelesscommunication device according to this embodiment has not reached thewireless reception device (at step A7).

Next, threshold A, threshold B, and threshold C used in thedetermination process according to the communication statecategorization algorithm shown in FIG. 2 will be described. Threshold A,threshold B, and threshold C depend on the performance characteristic ofan 802.11 wireless communication device. Threshold A, threshold B, andthreshold C correspond to determination criteria.

Threshold A is the minimum value of parameter dr of an 802.11 wirelessdevice when one 802.11 wireless device and another 802.11 wirelessdevice, as an interference source, simultaneously transmit respective802.11 reception devices and they can detect each other's transmission.

Threshold B depends on a wireless transmission rate. FIG. 3 shows thedependency of threshold B on wireless transmission rates. The dependencyof threshold B on the transmission rates can be obtained according tothe following procedure. First, an 802.11 wireless transmission deviceunder an environment of one communication link is caused to execute testtransmission at different transmission rates to an 802.11 wirelessreception device. Thereafter, the values of parameter bc at theindividual transmission rates are obtained. Finally, the values ofparameter bc and transmission rates are correlated. Threshold B isobtained by adding a predetermined offset to parameter bc. Thecommunication state categorization algorithm according to thisembodiment determines the communication state based on threshold B thatcorresponds to the test transmission rate shown in FIG. 3. FIG. 3 showsan example in which the offset is 10%. In FIG. 3, the values ofparameter bc that are measured under the environment of onecommunication link are denoted by squares and the values of threshold Bto which an offset of 10% is added are denoted by triangles.

Threshold C is the standard deviation of the values of parameter dr ofan 802.11 wireless device in a predetermined time when one 802.11wireless device and another 802.11 wireless device, as an interferencesource, simultaneously transmit other 802.11 wireless reception devicesand they cannot detect each other's transmission. Communication statecategorization section 4 stores the determined result to storage section3.

Next, with reference to FIG. 4, a specific example of the operation ofthe communication state categorization method for the wirelesscommunication device according to this embodiment will be described. InFIG. 4, it is assumed that wireless device A is the wirelesscommunication device according to this embodiment and that wirelessdevice B, wireless device C, and wireless device D are wirelesscommunication devices that comply with IEEE 802.11.

As shown in FIG. 4, it is assumed that wireless device A wirelesslytransmits 1500-byte (fixed length) packets to wireless device B located9 meters apart therefrom at a transmission rate of 54 Mpbs. In addition,it is assumed that wireless device C wirelessly transmits 1500-byte(fixed length) packets to wireless device D located 9 meters aparttherefrom at a transmission rate of 6 Mbps. Although it is preferredthat the transmission powers of wireless device A and wireless device Bbe fixed, they are not limited.

Packet transmission from wireless device A to wireless device B isreferred to as flow1, whereas packet transmission from wireless device Cto wireless device D is referred to as flow2. In this example, aninterference signal of flow2 to flow1 is considered as a detectiontarget. As flow2 is apart from flow1, the interference of flow2 to flow1weakens. In the example shown in FIG. 4, the intensity of aninterference wave of flow2 to flow1 is obtained by changing the distancebetween flow2 and flow1 from 1 meter to 200 meters so as to categorizethe communication state of wireless device A according to thisembodiment.

As flow2 starts moving from flow1 from a distance of 1 meter, datatransmission and reception section 12 of wireless device A startsexecuting the statistical process for the transmission and receptionparameters. Calculation processing section 2 of wireless device Acalculates the communication evaluation parameters bc, dr, and Std(dr)based on the transmission and reception parameters supplied form datatransmission and reception section 12 of wireless device A and storesthe calculated results to storage section 3. In the example shown inFIG. 4, the values of parameters bc and dr obtained by calculationprocessing section 2 of wireless device A are shown in FIG. 5 and FIG.6, respectively. The vertical axis of FIG. 5 represents the values ofparameter bc, whereas the horizontal axis represents the values ofdistance. A solid line shown in FIG. 5 is a line that connects theaverage values of the values of parameter bc. The vertical axis of FIG.6 represents the values of parameter dr, whereas the horizontal axisrepresents the values of distance.

Communication state categorization section 4 of wireless device A shownin FIG. 4 reads the communication evaluation parameters bc, dr, andStd(dr) from storage section 3 and categorizes the communication statesof wireless device A in flow1, that suffers from interference withflow2, according to the communication state categorization algorithmshown in FIG. 2, while flow2 is apart from flow 1 from 1 meter to 200meters. In the example shown in FIG. 4, threshold A and threshold C usedin the communication state categorization algorithm are calculated as80% and 0.12, respectively, according to the foregoing thresholdcalculation method.

The relationship between the transmission rate and threshold B obtainedaccording to the foregoing calculation method for threshold B is shownin Table 1. Parameter bc shown in Table 1 corresponds to threshold B.

TABLE 1 Data rate [Mbps] Busy count [%] 1 85 2 87 5.5 81 6 86 11 68 1280 18 73 24 73 36 65 48 56 54 59

In the example shown in FIG. 4, with reference to Table 1 obtainedaccording to the foregoing calculation method for threshold B, since thetransmission rate is 54 Mbps, threshold B is 59%. FIG. 7 shows thecategorized results of the communication states of wireless device A.The vertical axis of FIG. 7 represents communication states, whereas thehorizontal axis represents distance.

Next, the collision detection operation of the wireless communicationdevice according to this embodiment will be described.

Data transmission and reception section 12 shown in FIG. 1 transmitstest packets at a maximum transmission rate (for example, 54 Mbps) for aconstant time (for example, 3 seconds). At this point, collisiondetection section 5 counts the number of test packets that datatransmission and reception section 12 transmits and stores the countednumber as C1 to storage section 3. When data transmission and receptionsection 12 starts executing test transmission, signal sensing section 11senses the power of the spatial radio wave signal on the same channel asthe test transmission signal. After data transmission and receptionsection 12 has executed test transmission, signal sensing section 11stops sensing the power of the spatial radio wave signal and outputssample data of the sensed spatial radio wave signal to calculationprocessing section 2.

Thereafter, calculation processing section 2 converts the sample data ofthe spatial radio wave signal supplied from signal sensing section 11into time series power sample data. Calculation processing section 2stores the time series power sample data to storage section 3. In thefollowing, the time series power sample data are simply referred to as“time series sample data.”

Thereafter, collision detection section 5 reads the time series sampledata stored in storage section 3 and detects the foregoing interferenceif the wireless communication device according to this embodimentsuffers from interference with another 802.11 wireless device.

Next, with reference to FIG. 8 and FIG. 9A to FIG. 9D, the interferencedetection algorithm will be described in detail. FIG. 8 is a schematicdiagram showing an example of the interference detection algorithm. FIG.9A to FIG. 9D are schematic diagrams that describe a method that detectsa packet collision from the time series power sample data. The verticalaxis of each of FIG. 9A to FIG. 9D represents power, whereas thehorizontal axis represents time.

As shown in FIG. 8, the interference detection algorithm has averagepower calculation process 51, collision count statistic gatheringprocess 52, and collision rate calculation process 53. Collisiondetection section 5 is virtually configured by the CPU (not shown) ofarithmetic control section 8 that executes a program containing theinterference detection algorithm shown in FIG. 8. Thus, it is assumedthat the subject that executes each process shown in FIG. 8 is collisiondetection section 5.

First, the operation of average power calculation process 51 will bedescribed in detail. Collision detection section 5 calculates averagepowers shown in FIG. 9B as a first calculation based on the time seriessample data shown in FIG. 9A (at step B1). Specifically, collisiondetection section 5 calculates the average power of every N data piecesof the time series sample data that are read from storage section 3 (atstep B1). In the example shown in FIG. 9B, it is assumed that N=2. Blackcircles shown in FIG. 9A represent the powers of the sensed signals.

Thereafter, collision detection section 5 calculates average powersshown in FIG. 9C as a second calculation (at step B2). Specifically,collision detection section 5 successively checks for all data pieces ofthe powers obtained at step B1. If there is a data piece that is greaterthan threshold 1 and that immediately precedes (M−1) data pieces each ofwhich is greater than threshold 1, collision detection section 5 obtainsthe average value of the M data pieces and treats the obtained averagevalue as the average power of the M data pieces. In the example shown inFIG. 9C, M=5.

In contrast, if a data piece that is greater than threshold 1 isfollowed by M′ (that is smaller than (M−1)) data pieces each of which isgreater than threshold 1, collision detection section 5 obtains theaverage value of data pieces from “a first data piece of those whoseaverage power is greater than threshold 1” to “a data piece immediatelyfollowed by the first data piece of those whose average power is smallerthan threshold 1 (the last data piece of M′ (that is smaller than (M−1))data pieces whose average power is greater than threshold 1).”Thereafter, collision detection section 5 treats the obtained averagevalue as the average power value of data pieces from the first datapiece and the last data piece of those whose average power is greaterthan threshold 1.

In the same manner as the foregoing M data pieces and M′ (that issmaller than (M−1)) data pieces, collision detection section 5 calculateaverage powers as the second calculation until the end of data piecesthat correspond to the average powers obtained at step B1. In addition,collision detection section 5 substitutes the obtained average powerseach of which is smaller than the noise power threshold with L (forexample, three) successive 0's (at step B2). In the example shown inFIG. 9C, L=2.

In this example, N×M corresponds to the number of samples, K, of onetest packet transmitted at the maximum transmission rate. When N isaround 1% of K, an appropriate calculation accuracy can be obtained.Although threshold 1 depends on the performance of the device, threshold1 needs to be greater than the carrier sense threshold. In CSMA/CA, thecarrier sense threshold is used to determine whether or not a channel isbusy or idle. The carrier sense threshold is also referred to as theClear Channel Assessment level (CCA level). An appropriate noise powerthreshold is expected to be 1.5 times the noise average power. The noiseaverage power is obtained by a power measurement device. Besidesthreshold 1, threshold 2 is defined as a power determination criteria.Although threshold 2 depends on the performance of the device, threshold2 is obtained by multiplying threshold 1 by −1.

Collision detection section 5 obtains the power differences of adjacentdata pieces for all data pieces of the time series data obtained at stepB2 shown in FIG. 9C (at step B3). In other words, the value in which alater data piece is subtracted from an earlier data piece of twoadjacent data pieces is defined as the power difference of adjacent datapieces. FIG. 9D shows an example of the result. The upper side of thetime axis of FIG. 9D represents the plus side of power differences,whereas the lower side of the time axis represents the minus side ofpower differences. Black triangles shown in FIG. 9D represent powerdifferences of adjacent data pieces. FIG. 9D shows time series powerdifference data.

Next, the operation of collision count statistic gathering process 52will be described in detail.

At a collision detection step (step B4), collision detection section 5checks for time series data obtained at step B3 from the beginning. If adata piece that is greater than threshold 1 is immediately followed by“a data piece that is greater than threshold 1” rather than “a datapiece that is smaller than threshold 2” (this case is referred to ascase 1), collision detection section 5 counts this case as one packetcollision. If case 1 does not occur, collision detection section 5determines the next case. If threshold 1 needs to be greater than theCCA level and smaller than 50% of the power of a test packet, since nopacket collision occurs in case 1, collision detection section 5 doesnot determine whether or not case 1 occurs.

If Z data pieces that immediately precede a data piece that is greaterthan threshold 1 do not contain 0 (this case is referred to as case 2)or if Y data pieces that immediately follow a data piece that is smallerthan threshold 2 do not contain 0 (this case is referred to as case 3),collision detection section 5 counts this case as one packet collision.Although Z depends on the performance of the device, it is expected tobe 2. Likewise, although Y depends on the performance of the device, itis expected to be 5. However, if case 2 and case 3 succeed, namely if Zdata pieces that do not contain 0, immediately followed by a data piecethat is greater than threshold 1, immediately followed by a data piecethat is smaller than threshold 2, immediately followed by y data piecesthat do not contain 0, collision detection section 5 counts one packetcollision rather than two packet collisions.

On the other hand, if “a data piece that is greater than threshold 1(this data piece is referred to as “data piece P1” is immediatelypreceded by Z data pieces that contain 0 and if data piece P1 isimmediately followed by “a data piece that is smaller than threshold 2(this data piece is referred to as “data piece P2” immediately followedby Y data pieces that contain 0, collision detection section 5determines that this case corresponds to case 4 or case 5 that will bedescribed next and counts one packet collision. Case 4 is a case inwhich data piece P2 is immediately followed by “a data piece that issmaller than threshold 2” instead of “a data piece that is greater thanthreshold 1.” On the other hand, case 5 is a case in which data piece P2is immediately followed by “a data piece that is greater than threshold1” instead of “a data piece that is smaller than threshold 2” and theabsolute value of the sum of data piece P1 and data piece P2 is greaterthan threshold 3. Although threshold 3 depends on the performance of thedevice, it is expected to be equal to threshold 1. If neither case 4 norcase 5 occurs, collision detection section 5 determines that no packetcollision occurs. Collision detection section 5 stores the foregoingpacket collision count C2 in storage section 3 (at step B5).

Next, with reference to FIG. 9D, the packet collision detection methodin which collision detection section 5 detects a packet collision incase 4 will be described. In FIG. 9D, for the sake of description, datapieces that represent power differences of adjacent data pieces aredenoted by reference numerals 101 to 108.

Data piece 101 shown in FIG. 9D complies with the condition of datapiece P1 and data piece 102 complies with the condition of data pieceP2. However, since data piece 102 is immediately followed by data piece103 that is greater than threshold 1 rather than a data piece that issmaller than threshold 2, case 4 does not occur. In addition, data piece102 is immediately followed by data piece 103 that is greater thanthreshold 1. However, since the absolute value of the sum of data piece101 and data piece 102 is nearly 0 (<threshold 3), case 5 does not alsooccur.

Next, with reference to FIG. 9D, collision detection section 5 checksfor the data along the time axis. Since data piece 103 complies with thecondition of data piece P1 and data piece 104 complies with thecondition of data piece P2, collision detection section 5 determineswhether case 4 or case 5 occurs. With reference to FIG. 9D, since datapiece 104 is immediately followed by data piece 106 that is smaller thanthreshold 2 rather than a data piece that is greater than threshold 1,collision detection section 5 determines that case 4 occurs. Since datapiece 104 is immediately followed by data piece 105 that is smaller thanthreshold 1 and greater than threshold 2, data piece 105 is neither “adata piece that is greater than threshold 1” nor “a data piece that issmaller than threshold 2.” Thus, collision detection section 5 excludesdata piece 105 from the determination target.

In addition, with reference to FIG. 9D, collision detection section 5checks for the data along the time axis. Data piece 107 complies withthe condition of data piece P1 and data piece 108 complies with thecondition of data piece P2. However, in the observation time range ofthe time series data exemplified in FIG. 9, since data piece 108 is notimmediately followed by “a data piece that is greater than threshold 1”or “a data piece that is smaller than threshold 2,” collision detectionsection 5 does not need to determine whether or not a packet collisionoccurs.

Next, the reason why threshold 1 needs to be greater than the carriersense threshold will be described. FIG. 10A to FIG. 10D are schematicdiagrams that describe two types of packet collision patterns. Thevertical axis of each of FIG. 10A to FIG. 10D represents power, whereasthe horizontal axis represents time. In FIG. 10A to FIG. 10D,longitudinal rectangles represent powers of transmission packets of thetransmission terminal, whereas oblong rectangles represent powers ofinterference packets.

There are two types of packet collision patterns that are referred to asfirst and second patterns. FIG. 10A is a schematic diagram showing timeseries sample data of the first pattern, whereas FIG. 10B is a schematicdiagram showing time series power difference data in which envelopcharacteristics are extracted from the time series sample data shown inFIG. 10A. However, FIG. 10B schematically shows an interference packetshown in FIG. 10A so as to denote that an interference packet whosepower is lower than threshold 1 is a series of data pieces that are not0.

In the first pattern shown in FIG. 10A, the power of an interferencepacket is greater than the carrier sense threshold. In this case, eachtransmission terminal can correctly detect transmission packets of othertransmission terminals. Immediately after each transmission terminaldetermines that a channel is free, if the terminal transmits packets,packet collisions may occur as shown in FIG. 10A. As is clear from FIG.10B, packet collision pc1 shown in FIG. 10A corresponds to case 5 in theforegoing packet collision detection determination result. On the otherhand, packet collision pc2 shown in FIG. 10A corresponds to case 3 inthe foregoing packet collision detection determination result.

In FIG. 10B, it is likely that packet collision pc3 is not detected.This is because test packets preceded by packet collision pc3 are notobserved in the observation time shown in FIG. 10A. If test packets aredetected after packet collision pc3, “a data piece that is greater thanthreshold 1” in packet collision pc3 is immediately followed by “a datapiece that is greater than threshold 1” instead of “a data piece that issmaller than threshold 2” of the next test packet. Thus, packetcollision pc3 corresponds to case 1 in the foregoing packet collisiondetection determination result. Consequently, according to thisembodiment, it is clear that a packet collision of the first pattern canbe detected.

FIG. 10C is a schematic diagram showing time series sample data of thesecond pattern, whereas FIG. 10D is a schematic diagram showing timeseries power difference data in which envelop characteristics areextracted from the time series sample data shown in FIG. 10C. However,FIG. 10D schematically shows the interference packet shown in FIG. 10Cso as to denote that the interference packet whose power is lower thanthe carrier sense threshold is a series of data pieces that are not 0.

In the second pattern shown in FIG. 10C, the power of an interferencepacket is lower than the carrier sense threshold. In this case, sinceeach transmission terminal cannot correctly detect the transmissionpackets of other transmission terminals, it cannot correctly determinewhether or not a channel is busy. As a result, as shown in FIG. 10C, apacket that is transmitted by its own terminal collides with aninterference packet that it is unable to detect. The three packetcollisions shown in FIG. 10C correspond to case 2 or case 3 in theforegoing packet collision detection determination result, as is clearfrom FIG. 10D. Thus, according to this embodiment, a packet collision ofthe second pattern can be detected.

As was described with reference to FIG. 10, according to thisembodiment, since threshold 1 is greater than the carrier sensethreshold, the foregoing first and second collision patterns can bedetected.

Next, the operation of collision rate calculation process 53 will bedescribed in detail. Collision detection section 5 reads from storagesection 3 the number of test packets, C1, transmitted from the wirelesscommunication device according to this embodiment and the number ofpacket collisions, C2, and obtains the collision rate according toformula (2) that follows. Finally, collision detection section 5 storesthe calculated collision rate in storage section 3 (at step B6).

[Mathematical Expression 2]

Collision rate=C2/C1  Formula (2)

In formula (2), the right side denominator is the number of test packetsthat are transmitted, C1, and the numerator is the number of packetcollisions, C2.

FIG. 4 shows the experimental result of a collision detection operation.Likewise, it is assumed that wireless device A is the wirelesscommunication device according to this embodiment and that wirelessdevice B, wireless device C, and wireless device D are wirelesscommunication devices that comply with IEEE 802.11.

As shown in FIG. 4, it is assumed that wireless device A wirelesslytransmits packets to wireless device B that is located 9 meters apartfrom wireless device A. It is also assumed that wireless device Cwirelessly transmits packets to wireless device D located 9 meters apartfrom wireless device C. The packet transmission from wireless device Ato wireless device B is referred to as flow1, whereas the packettransmission from wireless device C to wireless device D is referred toas flow2. The interference signal of flow2 to flow1 is a detectiontarget. Thus, as flow2 is apart from flow1, the interference of flow2 toflow1 weakens.

In the example shown in FIG. 4, intensities of interference waves offlow2 to flow1 are obtained in six conditions in which the distancestherebetween are 1 meter, 10 meters, 40 meters, 80 meters, 110 meters,and 200 meters. Flow2 is successively moved to these six positions. Ateach position, wireless device A transmits 1500-byte (fixed length) testpackets to wireless device B at a transmission rate of 54 Mbps with atransmission power of 0 dBm for three seconds. At this point, wirelessdevice C transmits 1500-byte (fixed length) test packets at atransmission rate of 6 Mbps with a transmission power of 0 dBm for 3seconds. In this example, test transmission is executed with atransmission power of 0 dBm rather than the maximum transmission powerso as to attenuate the interference of flow2 to flow1 in a limitedmoving distance (200 meters).

Threshold 1 is set to 35% of the average power of the test packets. Inother words, assuming that the absolute value of the average power oftest packets is P, threshold 1 becomes (P×0.35). In addition, threshold2 is set to −35% of the average power of the test packets. In otherwords, when the absolute value of the average power of the test packetsis denoted by P, threshold 2 becomes −(P×0.35). In addition, threshold 3is set to 35% of the average power of the test packets. When theabsolute value of the average power of the test packets is denoted by P,threshold 3 becomes (P×0.35). Table 2 shows collision detection resultsin test packet transmission periods at individual positions.

TABLE 2 Number of Number of Packet collision transmission collisionDistance packets packets rate  1 m 71 437 16% 10 m 2196 2296 96% 40 m3922 4032 97% 80 m 3509 4294 82% 110 m  2432 5131 47% 200 m  1998 645631%

Table 2 tabulates the distances between flow 1 and flow2, the numbers oftransmission packets, the numbers of packet collisions, and the packetcollision ratios.

Next, the communication control operation of the wireless communicationdevice according to this embodiment based on the categorized result ofcommunication state categorization section 4 and the collision detectionresult of collision detection section 5 will be described in detail.

First, the communication control method of control section 6 based onthe categorized result of communication state categorization section 4of the wireless communication device according to this embodiment willbe described in detail. Control section 6 of the wireless communicationdevice according to this embodiment periodically checks for storagesection 3 and determines whether or not the communication state has beenupdated. If control section 6 determines that the communication statehas been updated, control section 6 outputs an operation command tocommunication section 1. Table 3 shows an example of operation commandsthat are output from control section 6 to communication section 1.

TABLE 3 communication state operation command PA Gray Operation command1 Change channel Change channel Operation command 2 Increase packet sizeDecrease packet size Operation command 3 Change Change communicationroute communication route

Table 3 tabulates communication states (PA and Gray) and correspondingoperation commands. Channel, packet size, and communication route are anexample of transmission parameters.

As tabulated in Table 3, there are three operation commands that areoperation command 1, operation command 2, and operation command 3.According to this embodiment, operation commands are assigned theirpriorities. Operation command 1 has higher priority than operationcommand 2; operation command 2 has higher priority than operationcommand 3. When the wireless communication device according to thisembodiment executes operation command 1, which is a channel changecommand, the wireless communication device can transmit a signal througha channel on which there is no interference signal or through a channelthat is less affected by another interference signal. If thecommunication state is PA, when the wireless communication deviceaccording to this embodiment executes operation command 2, which ispacket size increase command, the wireless communication device cantransmit much data in one transmission session and use a channel for alonger time and thereby improve the transmission efficiency. If thecommunication state is Gray, when the wireless communication deviceaccording to this embodiment executes operation command 2, which ispacket size decrease command, since the channel use time for thetransmission of one data packet decreases and the likelihood of acollision with another interference signal decreases, the transmissionefficiency improves. When the wireless communication device according tothis embodiment executes operation command 3, which is communicationroute change command, the wireless communication device can transmit asignal through another communication route in which there is aninterference signal or through another communication route in which theinfluence of an interference signal is low.

Next, with reference to FIG. 11, the communication control operation inthe case in which the communication state of the wireless communicationdevice according to this embodiment has been updated and in which onlyone communication state has been detected will be described in detail.

First, the case in which control section 6 detects that thecommunication state has been updated to state PA will be described. Ifcontrol section 6 detects that the communication state has been updatedto the state PA, control section 6 sends operation command 1“communication channel change command” to data transmission andreception section 12. When data transmission and reception section 12receives the command (operation command 1) from control section 6, datatransmission and reception section 12 quickly executes the operationaccording to the command (operation command 1). If data transmission andreception section 12 cannot execute the operation according to thecommand received from control section 6, data transmission and receptionsection 12 sends a signal that represents the failure of commandexecution to control section 6.

If control section 6 receives the signal that represents the failure ofcommand execution from data transmission and reception section 12,control section 6 sends operation command 2 “packet size increasecommand”, that has lower priority by one level than the precedingcommand, to data transmission and reception section 12. When datatransmission and reception section 12 receives the command (operationcommand 2) from control section 6, data transmission and receptionsection 12 quickly executes the operation according to the command. Ifdata transmission and reception section 12 cannot execute the operationaccording to the command (operation command 2) received from controlsection 6, data transmission and reception section 12 sends a signalthat represents the failure of command execution to control section 6.

If control section 6 receives the signal that represents the failure ofcommand execution from data transmission and reception section 12,control section 6 sends operation command 3 “communication route changecommand”, that has lower priority by one level than the precedingcommand, to data transmission and reception section 12. When datatransmission and reception section 12 receives the command (operationcommand 3) from control section 6, data transmission and receptionsection 12 quickly executes the operation according to the command. Ifdata transmission and reception section 12 cannot execute the operationaccording to the command (operation command 3) received from controlsection 6, data transmission and reception section 12 sends a signalthat represents the failure of command execution to control section 6.

If control section 6 receives the signal that represents the failure ofcommand execution from data transmission and reception section 12 and ifthere is no operation command that has lower priority than the precedingcommand, control section 6 will not transmit an operation command untilit detects that the communication state has been updated.

Thereafter, the case in which control section 6 detects that thecommunication state has been updated to the state Gray will bedescribed. If control section 6 detects that the communication state hasbeen updated to the state Gray, control section 6 sends operationcommand 1 “communication channel change command” to data transmissionand reception section 12. When data transmission and reception section12 receives the command (operation command 1) from control section 6,data transmission and reception section 12 quickly executes theoperation according to the command (operation command 1). If datatransmission and reception section 12 cannot execute the operationaccording to the command received from control section 6, datatransmission and reception section 12 sends a signal that represents thefailure of command execution to control section 6.

If control section 6 receives the signal that represents the failure ofcommand execution from data transmission and reception section 12,control section 6 sends operation command 2 “packet size decreasecommand”, that has lower priority by one level than the precedingcommand, to data transmission and reception section 12. When datatransmission and reception section 12 receives the command (operationcommand 2) from control section 6, data transmission and receptionsection 12 quickly executes the operation according to the command. Ifdata transmission and reception section 12 cannot execute the operationaccording to the command (operation command 2) received from controlsection 6, data transmission and reception section 12 sends a signalthat represents the failure of command execution to control section 6.

If control section 6 receives the signal that represents the failure ofcommand execution from data transmission and reception section 12,control section 6 sends operation command 3 “communication route changecommand”, that has lower priority by one level than the precedingcommand, to data transmission and reception section 12. When datatransmission and reception section 12 receives the command (operationcommand 3) from control section 6, data transmission and receptionsection 12 quickly executes the operation according to the command. Ifdata transmission and reception section 12 cannot execute the operationaccording to the command (operation command 3) received from controlsection 6, data transmission and reception section 12 sends a signalthat represents the failure of command execution to control section 6.

If control section 6 receives the signal that represents the failure ofcommand execution from data transmission and reception section 12 and ifthere is no operation command that has lower priority than the precedingcommand, control section 6 will not send an operation command until itdetects that the communication state has been updated.

Next, with reference to FIG. 12, the communication control operation inthe case in which the communication state of the wireless communicationdevice according to this embodiment has been updated and that twocommunication states have been detected will be described in detail.

If there are two or more interference sources, the communication statesPA and Gray may simultaneously occur. If control section 6 detects thattwo communication states of PA and Gray are occurring simultaneously andthat the communication state has been updated, control section 6 willsend operation command 1 “communication channel change command” to datatransmission and reception section 12. When data transmission andreception section 12 receives the command (operation command 1) fromcontrol section 6, data transmission and reception section 12 quicklyexecutes the operation according to the command (operation command 1).If data transmission and reception section 12 cannot execute theoperation according to the command received from control section 6, datatransmission and reception section 12 sends a signal that represents thefailure of command execution to control section 6.

If control section 6 receives the signal that represents the failure ofcommand execution from data transmission and reception section 12,control section 6 sends operation command 3 “communication route changecommand”, that has lower priority by one level than the precedingcommand, to data transmission and reception section 12. When datatransmission and reception section 12 receives the command (operationcommand 3) from control section 6, data transmission and receptionsection 12 quickly executes the operation according to the command. Ifdata transmission and reception section 12 cannot execute the operationaccording to the command (operation command 3), data transmission andreception section 12 will send a signal that represents the failure ofcommand execution to control section 6.

If control section 6 receives the signal that represents the failure ofcommand execution from data transmission and reception section 12 and ifthere is no operation command that has lower priority than the precedingcommand, control section 6 will not send an operation command until itdetects that the communication state has been updated. If controlsection 6 detects that the communication state has been updated to thestate Good, control section 6 will not send an operation command untilthe communication state has been updated.

Next, the communication control method of control section 6 based on thecollision detection result of collision detection section 5 of thewireless communication device according to this embodiment will bedescribed in detail.

Control section 6 of the wireless communication device according to thisembodiment periodically checks storage section 3 to determine whether ornot the collision rate has been updated. If control section 6 detectsthat the collision rate has been updated and that the collision rate isgreater than threshold 4, control section 6 sends a transmissionparameter adjustment command to data transmission and reception section12. When data transmission and reception section 12 receives thetransmission parameter adjustment command from control section 6, datatransmission and reception section 12 quickly adjusts the transmissionparameters according to the command. The transmission parameters includecarrier sensing sensitivity, back-off time, and the transmission rate.The back-off time is a transmission standby time for an 802.11 wirelessdevice. Threshold 4 depends on the performance of the device andcommunication application. For example, if the experiment shown in FIG.4 is conducted, control section 6 refers to the collision detectionresult shown in Table 2 and sets threshold 4 to 80%.

If the collision rate is greater than threshold 4, for example, ifcarrier sensing sensitivity is the transmission parameter, thetransmission parameter can be adjusted by improving the carrier sensingsensitivity. If transmission packet size is the transmission parameter,the transmission parameter can be adjusted by decreasing thetransmission packet size. If transmission rate is the transmissionparameter, the transmission parameter can be adjusted by increasing thetransmission rate. It is preferable that these transmission parametersbe selected and adjusted such that not only packet collisions can beprevented, but also such that the overall communication environment canbe improved.

If data transmitted from the wireless communication device according tothis embodiment interferes with another communication, the wirelesscommunication device will determine in which one of the threecommunication states its own device lies. The wireless communicationdevice can adjust the transmission parameters based on the determinedcommunication state so as to improve transmission efficiency.

In addition, before the wireless communication device according to thisembodiment starts transmitting data, it detects the occurrence of a testpacket collision in the neighboring radio waves, calculates thecollision rate of collisions, and appropriately adjusts the transmissionparameters based on the collision detection result and collision rate.Thus, the wireless communication device according to this embodiment canimprove the accuracy with which interference with another communicationis detected, can prevent interference with another communication, andcan improve transmission efficiency.

Second Embodiment

Next, with reference to the accompanying drawings, a wirelesscommunication device according to a second embodiment of the presentinvention will be described. For the sake of simplicity, a detaileddescription of structural sections similar to those of the firstembodiment will be omitted.

FIG. 13 is a block diagram showing an example of a structure of thewireless communication device according to this embodiment. As shown inFIG. 13, the wireless communication device according to this embodimenthas communication section 1, calculation processing section 2, storagesection 3, communication state categorization section 4, and controlsection 6. According to this embodiment, communication section 1 isprovided with data transmission and reception section 12 instead ofsignal sensing section 11 shown in FIG. 1.

The wireless communication device according to this embodiment is notprovided with signal sensing section 11 and collision detection section5 shown in FIG. 1. Thus, according to this embodiment, the transmissionparameters that improve the transmission efficiency are adjusted basedon the result that is output from communication state categorizationsection 4.

According to this embodiment, not only the transmission efficiency canbe improved, but also the circuit structure of the wirelesscommunication device can be simplified and thereby power consumption canbe reduced without necessity of adjusting the transmission parameter ofthe collision rate that is output from collision detection section 5shown in FIG. 1 or detecting collisions by collision detection section5.

Third Embodiment

Next, with reference to the accompanying drawings, a wirelesscommunication device according to a third embodiment of the presentinvention will be described. For the sake of simplicity, a detaileddescription of structural sections similar to those of the firstembodiment will be omitted.

FIG. 14 is a block diagram showing an example of the structure of thewireless communication device according to this embodiment. As shown inFIG. 14, the wireless communication device according to this embodimenthas communication section 1, calculation processing section 2, storagesection 3, collision detection section 5, and control section 6.

The wireless communication device according to this embodiment is notprovided with communication state categorization section 4 shown in FIG.4. Thus, according to this embodiment, the transmission parameter thatimproves the transmission efficiency is adjusted based on the resultthat is output from collision detection section 5.

According to this embodiment, not only can the transmission efficiencybe improved, but also the circuit structure of the wirelesscommunication device can be simplified and thereby power consumption canbe reduced without necessity of adjusting the transmission parameter ofthe communication state that is output from communication statecategorization section 4 shown in FIG. 1.

Fourth Embodiment

The wireless communication device according to the present invention canbe applied to a base station that composes a mesh network. According toa fifth embodiment of the present invention, the wireless communicationdevice according to the first embodiment is operated as a base stationof the mesh network. Next, the structure of the mesh network accordingto the fourth embodiment will be described.

FIG. 15 is a schematic diagram showing an example of the mesh network inwhich the wireless communication device according to the firstembodiment is configured as a base station. Circles shown in FIG. 15represent base stations. The locations of the base stations aredesignated based on a real application and according to an ordinaryinstallation method for mesh network base stations. One of a pluralityof base stations functions as a network communication management sectionthat manages communication in the network. In the following description,the network communication management section is referred to as themanagement station. In FIG. 15, the management station is denoted byreference numeral 7.

Next, the initial setup and operation for the mesh network according tothis embodiment will be described in detail.

The initial setup of the mesh network is performed in two stages of theadjustment of carrier sensing sensitivity of a base station and themeasurement of communication quality of a communication path. First,with reference to FIG. 16, the adjustment of carrier sensing sensitivityof a base station in the mesh network will be described in detail.

After the locations of base stations in the mesh network have beendesignated, one base station is selected as management station 7 thatmanages intra-network communication. Management station 7 isautomatically selected as a base station that has the minimum or maximumMAC address in the network. From a stability viewpoint, managementstation 7 needs to be preferentially selected from base stations thathave a power supply, an uninterruptible power supply, and an Ethernet(registered trademark) connection. Management station 7 that has beenselected transmits its own address to all base stations in the network.Each base station stores the address of management station 7 in storagesection 3. If management station 7 has been changed to another basestation, management station 7 that has been newly selected transmits itsown address to all base stations in the network and each base stationupdates the address of management station 7 stored in storage section 3.Although several selection methods for the management station wereexemplified, the present invention is not limited to these methods.

Thereafter, management station 7 sends a command to any one of basestations in the network so as to cause it to execute test transmissionat a constant transmission rate (for example, 6 Mbps) with a maximumpower (broadcast transmission) and to detect a collision (at step DD. InFIG. 15, a base station that executes test transmission is referred toas base station K1. The broadcast transmission is referred to astransmission TA. At this point, base stations other than base station K1are idle.

Thereafter, management station 7 sends a command to any one of the idlebase stations so as to cause it to execute test transmission on the samechannel as base station K1 in a full operation state (at step D2). Inthis example, “full operation state” means that base station K1continuously operates and it is assumed that the test transmission isbroadcast transmission. In this example, the base station that executesthe test transmission is referred to as base station K2. In thisexample, the broadcast transmission is referred to as transmission TB.The test transmission rate of base station K2 needs to be greater thanthe transmission rate of base station K1 (for example, 54 Mbps).

Thereafter, after base station K2 starts executing test transmission,management station 7 sends a command to base station K2 so as to causeit to detect a collision with test transmission executed by base stationK1 (at step D3). After base station K2 detects a collision, it storesthe collision rate of the test transmission executed by base station K1in storage section 3 (at step D4).

Thereafter, management station 7 sends a command to base station K2 soas to cause it to stop executing the test transmission and return to theidle state (at step D5). Base station K2 compares the collision ratestored in storage section 3 with threshold 4 (at step D6). If thecollision rate is greater than threshold 4, management station 7 adjuststhe carrier sensing sensitivity so as to prevent interference with basestation K1 (at step D7).

Thereafter, management station 7 successively sends a command to anybase stations other than those that have executed transmission TA andtransmission TB so as to cause them to execute the operation from stepD2 to step D7 (at step D8). The operation from step D2 to step D8prevents interference in the case that base station K1 and another basestation in the network simultaneously communicate with each other.Thereafter, management station 7 sends a command to base station K1 soas to cause it to stop executing test transmission and return to theidle state again (at step D9).

Thereafter, management station 7 successively transmits a command to anybase stations other than those that have executed transmission TA in thenetwork so as to cause them to execute the operation from step D1 tostep D7 (at step D10). The operation from step D1 to step D10 preventsinterferences of all base stations in the network with each other.

Next, with reference to FIG. 17, the communication quality measurementoperation for a communication path in the mesh network will be describedin detail.

First, management station 7 sends a command to any one base station H1in the network so as to cause it to execute test transmission for anyone base station H2 from among base stations that are in theneighborhood of base station H1 (at step E1). This test transmission isreferred to as transmission FA. Base station H1 executes testtransmission for base station H2 at a fixed transmission rate in thefull operation state. At this point, all base stations other than basestation H1 and base station H2 are idle. Thereafter, management station7 sends a command to any one base station H3 from among base stationsother than base station H1 and base station H2 so as to cause it toexecute test transmission for any one base station H4 from among basestations that are in the neighborhood of base station H3 (at step E2).It is assumed that this test transmission is unicast transmission. Thistest transmission is referred to as transmission FB. Base station H3executes test transmission for base station H4 at a fixed transmissionrate in the full operation state.

Thereafter, management station 7 sends a command to base station H1 soas to cause it to categorize the communication state of transmission FA(at step E3). After base station H1 has categorized the foregoingcommunication state, it sends to management station 7 information thatincludes the categorized result of the communication state oftransmission FA in the case in which transmission FB occurs, thetransmission rate of transmission FA, and the transmission rate oftransmission FB (at step E4). When management station 7 receives frombase station H1 the information that includes the categorized result ofthe communication state of transmission FA in the case in whichtransmission FB occurs, the transmission rate of transmission FA, andthe transmission rate of transmission FB, management station 7 combinesthese information as one set and stores it to storage section 3.

Thereafter, management station 7 determines whether or not base stationH3 has executed transmission FB at all transmission rates (at step E5).If base station H3 has not executed transmission FB at all transmissionrates, management station 7 sends a command to base station H3 so as tocause it to change the transmission rate of the test transmission to onein a predetermined range (at step E6). Thereafter, management station 7returns to step E2. “All transmission rates” means transmission rates inthe predetermined range, for example, those shown in Table 1.

If base station H3 has executed transmission FB at all transmissionrates (at step E5), management station 7 determines whether or not basestation H1 has executed transmission FA at all transmission rates (atstep E7). If base station H1 has not executed transmission FA at alltransmission rates, management station 7 sends a command to base stationH1 so as to cause it to change the transmission rate of testtransmission to one in the predetermined range (at step H1) and thenreturns to step E1.

If base station H1 has executed transmission FA at all transmissionrates (at step E7), management station 7 sends a command to base stationH3 and base station H4 so as to cause base station H3 to stop executingtest transmission and them to return to the idle state (at step E9).

While management station 7 is causing base station H1 to executetransmission FA at step E1, management station 7 determines whether ornot there is a base station that has not executed transmission FB (atstep E10). If there is a base station that has not executed transmissionFB at step E10, management station 7 selects base station H3(transmission side) that has not executed transmission FB and basestation H4 (reception side) (at step E11), sends a command to basestation H3 and base station H4 and then returns to step E2.

The operation from step E1 to step E10 allows management station 7 todetect the communication state of transmission FA in the case in whichtransmission FA at a particular base station and each communication pathin the network communicate simultaneously.

If there is no base station that has not executed transmission FB,management station 7 sends a command to base station H1 and base stationH2 so as to cause base station H1 stop executing test transmission andto cause these stations to return to the idle state (at step E12).Thereafter, management station 7 determines whether or not there is abase station that has not executed transmission FA (at step E13). Ifthere is a base station that has not executed transmission FA,management station 7 returns to step E1.

The operation from step E1 to step E13 allows management station 7 todetect the communication states in the case in which all communicationpaths in the network communicate with other communication paths atindividual transmission rates, correlates communication states andcommunication paths in all communication combinations, and stores thecorrelated information in storage section 3.

According to this embodiment, transmission FB at step E2 is unicastcommunication that base station H3 executes for base station H4.Alternatively, transmission FB may be broadcast communication that basestation H3 executes. If transmission FB is broadcast communication thatbase station H3 executes, base station H4 becomes idle at step E2.

Next, with reference to FIG. 18, the operation method for the meshnetwork according to this embodiment will be described.

When one of a plurality of base stations that compose the mesh networkaccording to this embodiment transmits data, the base station sends atransmission notification message that denotes that the base station isscheduled to transmit data to management station 7. In the followingdescription, a base station that is scheduled to transmit data isreferred to as base station 10. The transmission notification messagecontains information about a transmission route, through which basestation 10 is scheduled to transmit data, and information concerning thetransmission channel and the data transmission rate. If there is a basestation that is transmitting data before base station 10 transmits data,communication state information, that includes the transmission routethrough which base station 10 transmits data, the transmission channel,and the data transmission rate, has been stored in storage section 3 ofmanagement station 7. This information in the case of base station 10will be described later.

When management station 7 receives the transmission notification messagefrom base station 10, management station 7 reads communication states inthe case in which communication on a transmission route through whichbase station 10 is scheduled to transmit data interferes with existingcommunication in the network and sends a reply message that includes thecommunication state and transmission route of existing communication(interference route) to base station 10. Since correlated information ofall combinations of communication states and communication paths andcommunication state information of base stations that are transmittingdata have been stored in storage section 3, management station 7 canread the communication state of a transmission route through which basestation 10 is scheduled to transmit data from storage section 3.

When base station 10 receives the reply message from management station7, base station 10 stores information about the communication statecontained in the reply message as the communication state of thetransmission route through which base station 10 is scheduled totransmit data to storage section 3. Thereafter, control section 6 ofbase station 10 refers to Table 3 described in the first embodiment,reads an operation command corresponding to the communication statestored in storage section 3, and sends the operation command to datatransmission and reception section 12 so as to control communication ofdata transmission and reception section 12. After control section 6 hascontrolled the communication of data transmission and reception section12 and adjusted the transmission parameters, base station 10 sends atransmission ready message that denotes that it is ready to transmitdata to management station 7. The transmission ready message containsinformation about the transmission route, through which base station 10is scheduled to transmit data, and information concerning thetransmission channel and the data transmission rate.

When management station 7 receives the transmission ready message frombase station 10, management station 7 reads the information about thetransmission route, transmission channel, and data transmission ratefrom the transmission ready message and stores the information ascommunication state information of base station 10 in storage section 3.Thereafter, base station 10 starts transmitting data through thetransmission route on the transmission channel at the data transmissionrate concerning which base station 10 has notified the managementstation. After base station 10 has transmitted the data, base station 10sends a transmission completion message that represents the completionof the data transmission process to management station 7. Whenmanagement station 7 receives the transmission completion message frombase station 10, management station 7 deletes the communication stateinformation of base station 10 from storage section 3.

If management station 7 receives the transmission notification messagefrom base station 10, management station 7 always sends a reply messageto base station 10 within a predetermined time (for example, 3 seconds).After base station 10 sends the transmission notification message tomanagement station 7, if base station 10 cannot receive the replymessage from management station 7 within the predetermined time (forexample, 3 seconds), base station 10 quickly start transmitting data.

After base station 10 sends the transmission notification message tomanagement station 7, if base station 10 cannot receive the replymessage from management station 7 within the predetermined time, basestation 10 may send the transmission notification message to managementstation 7 after an elapse of a predetermined time (for example, 3seconds) again. In this case, after base station 10 sends thetransmission notification message to management station 7 apredetermined number of times including retransmission (for example,three times), if base station 10 cannot receive the reply message frommanagement station 7, base station 10 quickly starts transmitting thescheduled data. According to this embodiment, if base station 10 cannotreceive the reply message from management station 7, base station 10quickly starts transmitting the data. Alternatively, base station 10 maynot quickly start transmitting the data.

According to this embodiment, since a mesh network is composed ofwireless communication devices of the present invention, interferencebetween each communication path in the network can be prevented.

The foregoing first to fourth embodiments were described based on theIEEE 802.11 wireless LAN standard. However, it should be noted that thepresent invention is not limited to such a standard and LAN.

Alternatively, the wireless communication method according to thepresent invention may be executed by a computer. In addition, thewireless communication method may be applied to a program that causes acomputer to execute the method. The program may be stored in a recordmedium from which the computer can read the program.

According to the present invention, interference with anothercommunication can be prevented and thereby data transmission efficiencycan be improved.

While the invention has been particularly shown and described withreference to exemplary embodiments thereof, the invention is not limitedto these embodiments. It will be understood by those of ordinary skillin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present invention asdefined by the claims.

(Further exemplary embodiment 1) A wireless communication device,comprising: a data transmission and reception section that wirelesslytransmits a plurality of test packets; a signal sensing section thatsenses a power of a spatial radio wave signal on a frequency channelthat is the same as said plurality of test packets and outputs sampledata of the sensed spatial radio wave signal; a calculation processingsection that converts the sample data that are output from said signalsensing section into time series sample data in which the sample dataare plotted in time series; a collision detection section thatdetermines whether or not there is a packet collision due tointerference of said plurality of test packets with anothercommunication based on said time series sample data and calculates apacket collision rate based on the number of packet collisions and thenumber of said plurality of test packets that have been transmitted ifsaid packet collision occurs; and a control section that adjusts aparameter that said data transmission and reception section uses totransmit data based on a calculation result of said collision detectionsection.

(Further exemplary embodiment 2) A wireless communication device,comprising: a data transmission and reception section that wirelesslytransmits and receives packets and performs a statistical process fortransmission and reception parameters that are associated withtransmission and reception of the packets; a calculation processingsection that calculates communication evaluation parameters including abusy rate that represents a ratio of a time for which it is determinedthat a channel, that is the same channel as its own device, is used totransmit and receive packets, a packet transmission success rate, and astandard deviation of the packet transmission success rates based on aresult of the statistical process of said transmission and receptionparameters calculated by said data transmission and reception section; acommunication state categorization section that determines acommunication state that represents an influence rate of interferencewith another communication based on said communication evaluationparameters calculated by said calculation processing section; and acontrol section that adjusts parameters that said data transmission andreception section uses to transmit data based on a communication statedetermined by said communication state categorization section.

(Further exemplary embodiment 3) The wireless communication deviceaccording to Further exemplary embodiment 2, wherein said communicationstate categorization section determines that a non-interference state inwhich influence of interference with another communication is low occursif said packet transmission success rate is greater than a predeterminedfirst reference value and if said busy rate is equal to or smaller thana predetermined second reference value, determines that saidcommunication state is a communication anomaly state in which ancommunication anomaly occurs if said packet transmission success rate isgreater than said first reference value and if said busy rate is greaterthan said second reference value, and determines that said communicationstate is a communication interference state in which interference withanother communication occurs if said packet transmission success rate isequal to or smaller than said first reference value and if said standarddeviation of packet transmission success rates is greater than apredetermined third reference value.

(Further exemplary embodiment 4) The wireless communication deviceaccording to Further exemplary embodiment 3, wherein said controlsection causes said data transmission and reception section to changeany one from among a channel, a packet size, and a communication routeif said communication state is said communication anomaly state or saidcommunication interference state.

(Further exemplary embodiment 5) A wireless communication device,comprising: a wireless communication device according to Furtherexemplary embodiment 1; and a wireless communication device according toFurther exemplary embodiment 2, wherein said wireless communicationdevice according to Further exemplary embodiment 1 and said wirelesscommunication device according to Further exemplary embodiment 2 areintegrated.

(Further exemplary embodiment 6) A network, comprising: a plurality ofwireless communication devices according to Further exemplary embodiment5 arranged as base stations.

(Further exemplary embodiment 7) A wireless communication method,comprising: wirelessly transmitting and receiving packets and performinga statistical process for transmission and reception parameters that areassociated with transmission and reception of the packets; calculatingcommunication evaluation parameters including a busy rate thatrepresents a ratio of a time for which it is determined that a channel,that is the same channel as its own device, is used to transmit andreceive packets, a packet transmission success rate, and a standarddeviation of the packet transmission success rates based on a result ofthe statistical process of said transmission and reception parameters;determining a communication state that represents an influence rate ofinterference with another communication based on said communicationevaluation parameters; and adjusting parameters used to transmit databased on said determined communication state.

(Further exemplary embodiment 8) A computer readable record medium thatrecords a program that causes a computer to execute a process,comprising: wirelessly transmitting and receiving packets and performinga statistical process for transmission and reception parameters that areassociated with transmission and reception of the packets; calculatingcommunication evaluation parameters including a busy rate thatrepresents a ratio of a time for which it is determined that a channel,that is the same channel as its own device, is used to transmit andreceive packets, a packet transmission success rate, and a standarddeviation of the packet transmission success rates based on a result ofthe statistical process of said transmission and reception parameters;determining a communication state that represents an influence rate ofinterference with another communication based on said communicationevaluation parameters; and adjusting parameters used to transmit databased on said determined communication state.

What is claimed is:
 1. A wireless communication device, comprising: adata transmission and reception section that wirelessly transmits andreceives packets and performs a statistical process for transmission andreception parameters that are associated with transmission and receptionof the packets; a calculation processing section that calculatescommunication evaluation parameters including a busy rate thatrepresents a ratio of a time for which it is determined that a channel,that is the same channel as its own device, is used to transmit andreceive packets, a packet transmission success rate, and a standarddeviation of the packet transmission success rates based on a result ofthe statistical process of said transmission and reception parameterscalculated by said data transmission and reception section; acommunication state categorization section that determines acommunication state that represents an influence rate of interferencewith another communication based on said communication evaluationparameters calculated by said calculation processing section; and acontrol section that adjusts parameters that said data transmission andreception section uses to transmit data based on a communication statedetermined by said communication state categorization section.
 2. Thewireless communication device according to claim 1, wherein saidcommunication state categorization section determines that anon-interference state in which influence of interference with anothercommunication is low occurs if said packet transmission success rate isgreater than a predetermined first reference value and if said busy rateis equal to or smaller than a predetermined second reference value,determines that said communication state is a communication anomalystate in which an communication anomaly occurs if said packettransmission success rate is greater than said first reference value andif said busy rate is greater than said second reference value, anddetermines that said communication state is a communication interferencestate in which interference with another communication occurs if saidpacket transmission success rate is equal to or smaller than said firstreference value and if said standard deviation of packet transmissionsuccess rates is greater than a predetermined third reference value. 3.The wireless communication device according to claim 2, wherein saidcontrol section causes said data transmission and reception section tochange any one from among a channel, a packet size, and a communicationroute if said communication state is said communication anomaly state orsaid communication interference state.
 4. A wireless communicationdevice, comprising: a first wireless communication device; and a secondwireless communication device according to claim 1, wherein said firstwireless communication device, comprises: a data transmission andreception section that wirelessly transmits a plurality of test packets;a signal sensing section that senses a power of a spatial radio wavesignal on a frequency channel that is the same as said plurality of testpackets and outputs sample data of the sensed spatial radio wave signal;a calculation processing section that converts the sample data that areoutput from said signal sensing section into time series sample data inwhich the sample data are plotted in time series; a collision detectionsection that determines whether or not there is a packet collision dueto interference of said plurality of test packets with anothercommunication based on said time series sample data and calculates apacket collision rate based on the number of packet collisions and thenumber of said plurality of test packets that have been transmitted ifsaid packet collision occurs; and a control section that adjusts aparameter that said data transmission and reception section uses totransmit data based on a calculation result of said collision detectionsection, and wherein said first wireless communication device and saidsecond wireless communication device are integrated.
 5. A network,comprising: a plurality of wireless communication devices according toclaim 4 arranged as base stations.
 6. A wireless communication method,comprising: wirelessly transmitting and receiving packets and performinga statistical process for transmission and reception parameters that areassociated with transmission and reception of the packets; calculatingcommunication evaluation parameters including a busy rate thatrepresents a ratio of a time for which it is determined that a channel,that is the same channel as its own device, is used to transmit andreceive packets, a packet transmission success rate, and a standarddeviation of the packet transmission success rates based on a result ofthe statistical process of said transmission and reception parameters;determining a communication state that represents an influence rate ofinterference with another communication based on said communicationevaluation parameters; and adjusting parameters used to transmit databased on said determined communication state.
 7. A non-transitorycomputer readable record medium that records a program that causes acomputer to execute a process, comprising: wirelessly transmitting andreceiving packets and performing a statistical process for transmissionand reception parameters that are associated with transmission andreception of the packets; calculating communication evaluationparameters including a busy rate that represents a ratio of a time forwhich it is determined that a channel, that is the same channel as itsown device, is used to transmit and receive packets, a packettransmission success rate, and a standard deviation of the packettransmission success rates based on a result of the statistical processof said transmission and reception parameters; determining acommunication state that represents an influence rate of interferencewith another communication based on said communication evaluationparameters; and adjusting parameters used to transmit data based on saiddetermined communication state.